After the industrial revolution, people considerably utilized fuels, for example, coal, petroleum and natural gas, as a source of energy. The thermal energy generated from burning the above-mentioned fuels is converted into kinetic energy, and may be further converted into the electric energy. For example, steam engines, which boil the water by fuels, make the water change from a liquid phase to a vapor phase. Then, the water vapor propels a piston to move to produce mechanical work, which means the thermal energy in the boiling water is accordingly converted into kinetic energy. Moreover, the steam engines convert the kinetic energy into electric energy when the piston is further connected with an electromagnetic component. For another example, an explosion is generated inside a vehicle engine by means of the combustion of the air mixed with the gasoline extracted from the petroleum. After the explosion, the expanded air propels the piston and produces mechanical work, accordingly converting the chemical energy in the gasoline into kinetic energy. However, the fuel combustion, which converts chemical energy in the fuels into kinetic energy, also produces a large quantity of unnecessary thermal energy to dissipate outside. Therefore, the efficiency of the energy conversion from the chemical energy to the kinetic energy is not good enough, let alone the efficiency of the energy conversion from the kinetic energy to the electric energy.
Moreover, there is a shortage of the above-mentioned energy due to the increase of the human population. Even researchers have proposed the solutions of extracting petroleum from grains like sweet corn; nevertheless, those solutions may cause a food shortage. Therefore, it is necessary to seek renewable energy resources from nature in order to solve the shortage of an energy (e.g., wind power generation, hydraulic power generation and wave power generation).
However, renewable electricity production, from sources such as wind power and wave power, is sometimes criticized for being variable or intermittent. Therefore, how to acquire stable energy from the natural environment is a problem that researchers from the related industry try to solve.